Incorporating real-time image guidance into radiotherapy can improve tumour targeting accuracy, enabling better avoidance of critical structures and reducing side effects. Such guidance is of particular benefit if a non-ionizing imaging technique such as MRI (magnetic resonance imaging) is employed. Work is currently being undertaken to integrate a linear accelerator with an MR scanner. By integrating high-quality MRI with a source of therapeutic radiation, such as a linear accelerator, tissue can be tracked online and therapeutic radiation beams can be guided to their targets (which may be moving and deforming, such as when the patient breathes) with sub-millimetre precision during treatment.
Radiotherapy frequently utilises various devices and accessories to position a patient; these can include couches, patient supports and replaceable top surfaces therefor, head frames in all types of radiotherapeutic apparatus and (in the case of an MR-Linear Accelerator (MRL), where the patient is also imaged) RF imaging coils and associated stands, etc. If these accessories are located in the path of the radiotherapeutic beam, they may affect the efficacy with which the beam provides the therapy to the patient. There is often a predetermined treatment plan for a particular patient, with an automated treatment planning system (TPS) controlling the relative positions and/or orientation of the patient, the MR scanner and the linear accelerator, and the radiation produced by the linear accelerator to achieve this plan, based on images obtained from the MR scanner. However, non-biological objects such as the devices/accessories will not usually be clearly visible to an MR scanner, and thus cannot be taken into account in an automated treatment planning process; accordingly an operator has to carefully locate and orientate such devices prior to treatment, and manually input information of their location, orientation and composition into the TPS in order for the radiotherapy to be applied in accordance with the predetermined treatment plan. This is time-consuming, and does not account for any movement which may occur during a radiotherapy treatment.